Recent Advances in Dental Resin Composites PDF

Recent advances in dental resin composites Professor Dr Asmaa Aly Yassen 2022  Recent advances in dental resin composites The era of dental composites began about 1954 as follows; Silicate cements Unfilled methyl methacrylate resins Adhesive epoxy resi...

Recent advances in dental resin composites Professor Dr Asmaa Aly Yassen 2022  Recent advances in dental resin composites The era of dental composites began about 1954 as follows; Silicate cements Unfilled methyl methacrylate resins Adhesive epoxy resins became available. The slow hardening of epoxy formulations led to the synthesis of Bis- GMA in 1956 The term “composite material” refers to a material made up of at least two distinct components, insoluble in each other, which produce a material with different, often better, characteristics than the components alone. The main components of dental composites are (1) The organic resin matrix (2) Inorganic filler particles are distributed (3) Silane coupling agent that coats the filler particles for chemical bonding to the resin matrix. (4) Initiators/ Activators for the onset of polymerization reaction. (5) Inhibitors that prevent spontaneous polymerization (6) Pigments for tooth-matching color range. Demands for continuous improvement of dental composites: 1) Improvement of the mechanical properties. 2) Enhancement of esthetic outcome. 3) Overcome the problem of polymerization shrinkage and the induced stresses. 1  4) Maximize their adaptation to cavity walls and margins and subsequently minimize the problem of microleakage. 5) Simplification of their application and making them less technique sensitive. 6) Minimize the problem of thermal mismatch with the tooth structure. 7) Obtaining highly biocompatible and bioactive materials. Commercial dental composites, indicated for restoring anterior teeth, were introduced in the mid-1960s. The following decades of composite development can be broadly divided into three main periods. 1. Curing Modifications a) Self-cured or Chemically cured Composite: Early composites consisted of two pastes which initiated the curing reaction on mixing. As no external factor was involved in the curing process, these composites were called “self-cured” or “chemically cured.” 2  The two pastes were based on: v BisGMA resin matrix diluted with liquid monomers, primarily TEGDMA. v Suspended 70–80 wt% of quartz, borosilicate, ceramic, or glass particles, irregularly shaped and up to 100 μm in diameter [Macrofillers]. The use of such macrofilled composites in posterior teeth was not recommended. Indications for the use of macrofilled composites were primarily Class III and V. Disadvantages: v Low wear resistance leading to the loss of anatomic form. v Very bad esthetics v Self-cured composites were hand-mixed which could lead to errors in paste concentrations and inclusion of air bubbles in the polymer, resulting in compromised material properties. B) Light-cured composites: They were introduced in mid-1970s. This allowed composites to be prepared as one paste with precisely defined composition by the manufacturers. UV light cured composite: The first light-cured composites required UV light sources, operating between 360 and 400 nm, to initiate polymerization. The drawbacks of UV lights included v Health hazard to eye and oral tissue. v Rapid deterioration of light intensity. v Shallow penetration resulting in inferior depth of cure of UV-cured composites. 3 Visible light-cured composites : In the late 1970s, they were introduced with the potential to overcome the drawbacks of UV-cured composites. The new photo initiator system based on camphorquinone with tertiary amine co initiator provided higher monomer-to-polymer conversion than that of self- cured composites with no drawbacks associated with UV lights. Dual cured composites: They are cured with both chemical and light activation and they are used in core buildup or cementation purposes. Heat cured composites: Especially for indirect restorations. 2. Filler Modifications Macro Midi Mini Micro Nano 100 10 1 0.1 0.01 0.005 a) Macrofilled composites: They are the first developed composites contained filler particles in the range of 10–50 μm even up to 100 μm. Macrofilled composites are more susceptible to discoloration and difficult to polish because when filler particles at the surface are lost (due to wear or erosion ) the surface becomes very rough. This disadvantage reduces the uses of this type of composites. b) Midifilled resin composites. They are the next generation after the early macrofilled composites which had fillers that range from 1-10 μm. The category soon became known as traditional or conventional composites, but newer composites continue to evolve with even smaller particle size range. 4 c) Minifilled resin composites: The principle particle size for these composites was in the 0.1 to 1 μm range. d) Microfilled resin composites ( Late 1970's): They were developed to achieve a more polishable restoration ( fine finishing composites).They are composed of light activated, dimethacrylate resins with colloidal silica fillers averaging 0.01 μm with a filler loading of 32% - 50% by volume. The small filler particle size produced high viscosities and required the addition of greater amounts of monomer diluents TEGDMA, along with a reduced overall filler content to maintain workable consistencies. To counteract the viscosity problem two strategies were developed: First: Heterogenous microfills ( organic filler composites ) Blend precured microfill composite with uncured material. Precurred particles were generated by grinding cured composites to a 1 – 20 μm sized powder. The precured particles become chemically bonded to the new materials. N.B : unmodified microfills are called homogenous microfills. 5 Second: Sintering Small filler particles have been sintered into large but porous filler particles, impregnate them with monomer , and add the new particles to a microfilled composite. Problems associated with the microfilled composite: (A) Resin filler / Matrix interface. The interface between the prepolymerized resin filler and the surrounding matrix has been thought to be a weak link. Since the prepolymerized resin fillers are highly cured, they cannot copolymerize with the surrounding resin matrix. This weak bond can result in filler loss and decreased tensile strength (B) High coefficient of thermal expansion (Low filler content). (C) Low tensile strength (Indicated in non-stress bearing areas as cl III &V) (D) High water sorption (High resin content). (E) High polymerization shrinkage. (F) Low stiffness and fracture resistance. Hybrid composites: In the early 1980s, hybrid composites were introduced as a true combination of macrofilled and microfilled composites. They contained macrofiller quartz, glass, or Ba/Sr/Al/Zr-silicate particles (1–50 μm) with amorphous silica microfiller particles (0.04 μm). The tendency over the 1980s was to further reduce the size of macrofiller particles to an average of 1–5 μm (midifills) or 0.6–1 μm (minifills). Hybrid composites were 6 considered an optimal combination for favorable mechanical and optical properties and improved wear resistance. They were termed universal composites as they are indicated to be used anteriorly and posteriorly. Quartz: was being replaced with other types of fillers due to its high abrasiveness toward enamel and lack of radiopacity. In mid- and late 1990s, two different “classes” of composite materials were developed, based on their consistency; Flowables and Packables Flowable composites were designed for better adaptation in deep or undercut areas of the cavity. Their low viscosity is achieved by either lowering the filler content or adding surfactant. The mechanical properties of flowables were significantly worse than those of universal composites which restricted their field of indications to v Cavity lining v Small restorations at load-free areas (e.g., Class V) v Restoration repair. Examples: (Filtek 350 XT flowable,3M ESPE/ Tetric flow, vivadent) NANO-FILLED FLOWABLE COMPOSITES ü Utilizes nanosized fillers ü Still flows readily ü Excellent esthetics ü Low Wear in comparison to non filled or microfilled flowable composite. ü Available in compules 7 Example; (SDR, Dentsply/ Filtek Supreme Ultra Flowable, 3M ESPE/ Herculite Ultra flow and Premise, Kerr) Packable composites were designed specifically for posterior teeth as a potential amalgam replacement. Packability was achieved in different ways maintaining the filler content in the range of 75–85 wt%: (1) Fused particle agglomerates (sintering) (2) Fibrous fillers (3) Narrow distribution of midi-, mini-, and microfillers. The mechanical properties of early packable composites were not improved nor the polymerization shrinkage reduced as would be expected of high-density materials. Examples: Surefil, Dentsply/ Solitaire, Heraeus Kulzer/ AlertTM, Pentron) Nanofilled composites Nano-filled resin composite has been introduced, to develop a dental resin composite that had ý The mechanical strength of hybrid composite material ý The superior polish and gloss retention associated with micro-filled materials. Nanofilled composites contain silica and/or zirconia particles in the form ý Nanomers spherical discrete/non-agglomerated particle (avg. size 5– 20 nm) ý Nanoclusters spheroidal fused/ agglomerated nanoclusters (avg. size = 0.6– 10 μm). 8 Optical properties of Nanofilled resin composites: The size of nanomeric particles is < wave length of the visible light (400-800 nm), which: ü Makes them non measurable by refractive index. ü Provides the opportunity of creating highly translucent materials. ü Improved the depth of cure and the consequently the degree of conversion DC. ü Wide range of shades and opacities restoration (Optimal esthetics) is achieved by adding microfillers and nanoclusters (Nanohybrid). Nanohybrid composites contain 1. Silica/ Zirconia nanoparticles 2. Larger 0.6–1 μm microfiller glass/ zirconia/silica particles. 3. prepolymerized resin fillers 4. nanoclusters. The new technology used to create nano-sized filler particles allowed greater nanofiller content compared to the traditional microfilled composites. Filtek Z 250 XT ( 3M ESPE) is composed of nanomeric particles and nanoclusters. The use of spheroidal nanocluster fillers with a broad particle distribution provides a higher filler load, desirable handling characteristics, and physical properties comparable with conventional hybrid composites. During abrasive wear, the nano-sized primary particles in the nanocluster are suggested to wear by breaking off individual primary 9 particles, rather than be plucked out, resulting in wear surfaces which have smaller defects and thus better gloss retention. In comparison, the wear of hybrids and microhybrids has larger discrete filler particles and thus larger defects and therefore has less polish retention. This composition provides improved clinical performance through an 1. Increased polishability 2. Increased wear resistance 3. Reduced polymerization shrinkage 4. Increased fracture resistance. 5. Reduced viscosity in the resin matrix, thus the filler loading that can be attained is high. 6. Inhibiting crack formation and propagation. 7. The spheroidal shape provides smooth and rounded edges distributing stress more uniformly throughout the composite resin. This phenomenon has been termed the “roller bearing” effect, and is said to improve the sculptability and handling characteristics. Premise, Kerr (Trimodal filler system): The nanocomposite is composed of three different types of filler components: 1. Non agglomerated discrete silica nanoparticles (3 distinct filler sizes) 2. Barium glass fillers for better blending (hard to detect) 3. Pre-polymerized filler (limits shrinkage and enhances polishability and wear resistance). 10 Neo Spectra universal, Dentsply [SphereTEC Filler Technology] The key improvements in this composite were made possible by SphereTEC filler technology, the proprietary method of manufacturing microscaled, well-defined spherical superstructures, comprised of submicron glass. The SphereTEC fillers’ morphology, particle size distribution and surface microstructure deliver the benefits that really matter to dentists: Optimized handling for easy placement and shaping (Roller bearing). Enhanced chameleon blending ability for simplified shade selection and matching. (Take the color of the surrounding tooth tissues) Improved durability with high polish and stain resistance for lasting esthetic. NB: including fillers with refractive index of 1.53 into BisGMA/ TEGDMA resin with RI 1.52 resulted in RC with a perfect color matching (Same light transmission, reflection, and absorption) with the surrounding structure (Chameleon effect). 11 Harmonize [Kerr] (Adaptive Response Technology ART) Two ways in which Harmonize adapts its behavior to meet certain conditions. ý The rheological additive causes the handling to adapt to the clinician’s behavior. It is soft and easy to sculpt without being sticky when manipulated with an instrument and regains viscosity when at rest. ý It also adapts to the light wavelength by reflecting diffuse light at lower wavelengths and specular light at higher wavelengths to better match natural enamel. This adaptive response provides crucial clinical performance and is totally unique to Kerr. Harmonize elevates the esthetic capabilities of the clinician. Fiber reinforced resin composite This type of composite contains fibers, optimally sized for maximum strength and fracture resistance (Crack Arresting property). It should always be overlaid with an external nanofilled resin composite material. It can be applied in 4mm thickness. It is used in the biomimetic dentistry. Example: everX posterior, GC America NB: Individual silanated fibers are available in the market to reinforce the resin composite material. 3. Resin Modifications Most of the developments have focused on the filler systems, leading to improvements mainly in mechanical properties and notably on wear resistance. Irrespective of these improvements, the average life span of a composite restoration is still only around 10 y. 12  In the early 2000s, greater attention was focused on the further development of the organic matrix, which to date had been based exclusively on methacrylate chemistry, more specifically BisGMA (bisphenol A glycidyl dimethacrylate) TEGDMA (triethylene glycol dimethacrylate) BisEMA (ethoxylated bisphenol-A dimethacrylate) UDMA (urethane dimethacrylate). Low shrinkage composite: Alternative monomers began to be developed with the common objective of reducing polymerization shrinkage and stress, as the possible association between stress development and gap formation at the bonded interface was being emphasized. The new monomers were either based on 1. Ring-opening polymerization (with the only commercial example being Filtek P90 LS,3M ESPE, based on Silorane chemistry) 2. Higher molecular weight methacrylate based molecules (Aelite LS, Bisco & Venus Diamond, Heraeus Kulzer) Both strategies were successful at reducing the polymerization shrinkage and the polymerization stress. Clinical studies, however, have failed to show differences between the “low-shrinkage/low-stress” materials and their conventional counterparts in terms of restoration survival and incidence of secondary decay. 13 This is likely due to the ü Multifactorial nature of caries development ü The overall technique sensitivity of the restorative procedure ü The silorane resin is more hydrophobic than methacrylate resins, so: à Decreased Water uptake à Decreased Wettability and adaptation Ormocers (organically modified ceramic) In contrast to conventional composites, the Ormocer matrix is not only organic but also inorganic. Ormocers basically consist of three components 1. The organic polymers influence the ability to cross link, hardness and optical behavior. 2. The glass and ceramic components (inorganic constituents) are responsible for thermal expansion and chemical stability. 3. The silicone influence the elasticity and interface properties. Their performance was significantly worse when compared to today’s hybrid composites. Example: AdmiraR Flow/Fusion, Voco Fusion Gingiva Aesthetic Pink composite It is a nanofilled composite with pink pigments and it is used to treat cervical defects and exposed, discolored or hypersensitive necks of the teeth. 14 Trials to minimize the technique sensitivity: a) Bulk fill Composite: They have been introduced to the market in both flowable and conventional/sculptable viscosities, with the premise of simplified application, while still ensuring adequate depth of cure. This has been achieved for different commercial materials via different routes, which include; ü Optimization of the initiator system (novel photoinitiators or greater concentration of conventional photoinitiators) Tetric EvoCeram Bulk-Fill (Ivoclar Vivadent) uses a photoinitiator system containing Ivocerin—a germanium-based light initiator, whose produces a great conversion and promoting deep polymerization. ü Modifications of the filler system (larger fillers or more translucent fillers) ü Polymerization modulator: A photoactive groups embedded in the backbone of an oligomer. Under light exposure this group undergo photo-cleavage and generates radicals which contribute to further conversion and cross linking of the material. Filtek Bulk-Fill (3M-ESPE), It has monomer which is capable of undergoing addition fragmentation (bond breakage and re-formation). Flowable bulk-fill materials generally have lower filler loading than nonflowable (sculptable) materials and require that the occlusal layer be filled with a “cap” of a more highly filled composite that is expected to be stronger and more wear resistant under occlusal loading. One example is SureFil SDR flow (Dentsply). It is based on polymerization modulator. 15 Sonicfil™ (Kerr), It consists of a bulkfil composite resin and a sonic handpiece that fits onto a traditional high speed hand-piece. The sonic energy generated causes a dramatic change in the viscosity of the composite resin so that during placement, it behaves similarly to a flowable liner in its ability to adapt to the internal surfaces of the cavity preparation. Although the restorative material is around 86% filled by weight, special additives in the composite allow the filler particles to slide very readily over one another when activated by the sonic energy in the handpiece. Once the sonic energy is removed, the composite resin gradually returns to a higher viscosity, which is suitable for sculpting the restoration to its most precise morphologic form. The material is then light cured and finished using traditional techniques. ü It allows composite placement up to 5 mm in depth in a single increment, without any liner or capping layer as it is flowable during placement. b) Self-Adhesive Composites and Resin Cements ü Examples: Vertise Flow , Dyad Flow (Kerr Corporation), ,FusioTM, Pentron and Rely X, 3M. All commercial self-adhesive resin- based materials commercialized to date are flowable (i.e., materials designed to enhance adaptation to the substrate by their low viscosity) ü Goal……. simplifying the composite restorative procedure by eliminating its most technique-sensitive step: the adhesive application 16 ü The resins in these composites contain a self-etching, dimethacrylate monomer capable of; a) Crosslinking and copolymerization with other methacrylates b) Chemical bonding with the tooth’s mineral content. c) Micromechanical interlocking between polymerized monomers and partially demineralized collagen fibrils. ü Bond strength values of resin-based self-adhesive cements and restorative flowable composites are not as high as those achieved with separate adhesives and composite restoratives to tooth structure. This has been attributed to; a) The acidity of the monomers in the self-adhesive materials is not low enough to promote extensive resin penetration through smear- covered surfaces or into enamel. b) The viscosity presented by flowable materials is not low enough to ensure good adaptation to the cavity walls. c) High water sorption, as well as increased microleakage Self-adhesive composite hybrid has been launched under the brand name Surefil one (Dentsply Sirona). It combines the convenience of a glass ionomer with the durability of a composite. A modified polyacid system of high molecular weight (MOPOS) has been formulated to merge the self-adhesive properties of classical polyacids known from glass ionomer cements with the crosslinking ability of structural monomers known from composites. It is dual cured material. 17 c) Thermoviscous Composite with Dispenser 1. Composite with effective handling dispenser. 2. Provides quick and homogeneous heating using the infrared technology. 3. It is characterised by its bubble-free application. Example; Viscalor Bulk d) Minimizing Steps of application with maximum esthetics: ESTELITE ASTERIA, Tokuyama RAP technology (Rapid Amplified Photopolymerization initiator) Unlike multilayer techniques used with conventional composites, ESTELITE ASTERIA uses only 2 layers for optimal results (Body and Enamel). Body shades have excellent blending ability and provide translucency with sufficient opacity to avoid shinning through without the use of opaquer or dentin shades. It contains 82% by weight silica- zirconia filler and composite filler. Every inorganic filler is spherically shaped (mean particle size 200nm). This Supra-Nano spherical filler facilitates a very smooth surface with superior gloss that is easily obtained with polishing and is sustained long-term. A high filler load offers decreased polymerization shrinkage and competitive wear resistance. It offers a quick (reduced) curing time and an extended working time under the operatory light by “Radical Amplified Photopolymerization (RAP) Technology”. It has excellent handling properties; it is not sticky and easy to sculpt. 18  Omnichroma,Tokuyama It is a monoshaded (No pigments) type of composite with an excellent shade matching due to reflection of underlying tooth structure shade. It uses 260nm spherical filler which generate color parameter necessary to match the tooth. NB: In case of absence of background as class III through and through or class IV blocker should be applied first to mask the darkness of the oral cavity. Trials to obtain bioactive resin composite: a) Giomer: (glass ionomer polymer) This resin composite has the fluoride release of GICs by means of their unique surface pre-reacted glass (S-PRG) filler. The glass ionomer phase in Giomer fillers is protected from water sorption and material degradation by a surface modified layer. As a result, the ion exchange from a composite material that incorporates this technology can neutralize acids that result from bacterial metabolism and that are a direct cause of tooth demineralization. It releases Fluoride, Strontium, Sodium, Aluminum, Silicate and Boron. ý Fluoride: fluoroapatite formation/ Remineralization/ Antibacterial effect ý Boron: Antibacterial effect ý Strontium: Remineralization ý Silicate: Remineralization ý Aluminium: Dentin sealing (eg, Beautifil® II, Beautifil-Bulk Restorative two consistencies, Flowable (Zero and low flow), Beautifil® II low shrinkage/ Shofu). 19 FIT SA (Shofu): It is a self adhesive flowable composite with bioactive Giomer technology. b) Antimicrobial composite materials v One of the main reasons for composite restoration failure is secondary caries development, mainly related to biofilm formation on and within gaps at the restoration margins. v Antimicrobial materials have its effect by a) Kill the bacteria on contact (bactericidal effect) and/or b) Prevent bacterial adhesion (antifouling effect) v The mechanical properties don't being affected. Some examples of commercial antibacterial materials are (Clearfil SE Protect, Kuraray Dental) adhesive that contains MDPB and Activa BioActive-Restorative resin composite (Pulpdent) v Nanoparticles of silver, zinc oxide, and gold to inhibit development of the S. mutans strains. Silver nanoparticles is the most effective for controlling S. mutans and therefore caries. c) Remineralizing Materials The introduction of such materials aim to regain the lost mineral content from early disease to prevent cavitation of the lesion. Examples for nanoparticles have been widely studied as remineralizing agents: a) Calcium fluoride (nCaF2) b) Amorphous calcium phosphate (nACP) c) Nanohydroxyapatite (nHA) d) Nanofluorohydroxyapatite (nFHA) Example: HyperFil HAp 20 Future development Self-healing composite: If a crack occurs in the composite material, some of the microcapsules are destroyed near the crack and release the resin. The resin subsequently fills the crack and reacts with a catalyst dispersed in the epoxy composite, resulting in a polymerization of the resin and repair of the crack. Stress-Reducing Materials Stress-reducing materials continue to be the focus of investigations due to their utility in preventing gap formation at the tooth-restorative material interface. a) The development of thiourethane oligomers (Delayed gelation and cross linking) b) Nano-sized prepolymerized particles c) Monomers with addition fragmentation Degradation-Resistant Materials The main disadvantages of the resin matrix are 1. Incomplete conversion and water sorption decrease the stability of the polymer matrix and contribute to the less than optimal clinical lifetime. 2. Hydrolysis via their ester bonds, a process that can be accelerated at higher temperatures and low pH, which in turn are conditions of the oral environment. To address these shortcomings, materials rather than methacrylate chemistry should be used as restorative composites. 21